1. Field of the Invention
This invention relates generally to communication systems, and, more particularly, to wireless communication systems.
2. Description of the Related Art
A conventional wireless communication system provides wireless connectivity to numerous access terminals such as the cellular telephones, personal data assistants, smart phones, pagers, text messaging devices, global positioning devices, notebook computers, desktop computers, and the like. For example, access networks in the wireless communication system may provide wireless connectivity to access terminals located in geographical areas, or cells, associated with the access networks. To initiate a call session, an idle access terminal transmits a call request (or connection request) to one or more access networks to provide wireless connectivity to the cell that includes the access terminal. If the access network has sufficient capacity to support a new call, then the access network may transmit a message granting the access terminal's call request. The requested call session may be initiated and the access terminal may enter the active state. However, not all call requests are granted.
A call request from an access terminal may be denied because the system is overloaded and lacks sufficient capacity to support a new call. For example, the access network may not have sufficient radio frequency resources to support an air interface between the access network and the access terminal and may therefore deny the request. In other situations, there may not be sufficient backhaul capacity to support adding an additional call in the wireless communication system. In yet other situations, the processor occupancy associated with processors in the base station or access network may be too high to support an additional call. When the call request from an access terminal is denied, the access network transmits a message to the access terminal indicating that the call request has been denied. Access terminals typically respond to a call request denial using an apersistence procedure in which the access terminal waits for a random period of time (i.e., the apersistence value) before starting the access procedure again.
Access terminals typically support applications that implement Grade of Service (GoS) features and/or Quality of Service (QoS) features. For example, some applications may offer premium priority services or special family focused programs. Likewise, service providers attempt to support business sector and public sector applications such as emergency calls, priority calls (in both business and public sectors), providing police patrolling support, fire worker emergency support, a privileged level support for business leaders and commanders and enabling group communication activities. Some of the requirements associated with such applications include supporting different levels of priorities for access and admission, supporting different levels of priorities in an overload control condition, and accounting for different GoS/QoS levels in resource allocation decisions.